1. Field of the Invention
The present invention relates to an improved magnetic disk drive and more particularly to a thin film magnetoresistive head in the disk drive which is protected from: (1) electrical shorting across its thin film layers at an air-bearing surface, and (2) electrical shorting between its thin film layers at the air-bearing surface and a disk rotating therebelow.
2. Discussion of the Related Art
In the electromagnetic recording arts, thin film flux sensing heads are more desirable than inductive heads because of their higher areal density capability. They are also easier to manufacture. With various thin film manufacturing techniques, they can be fabricated in batches on a substrate and then cut into individual units. A read head employs a magnetoresistive element which changes resistance in response to magnetic flux density from a rotating magnetic disk or a moving magnetic tape. A sensing current, which is passed through the magnetoresistive element, varies proportionally to the change in resistance of the magnetoresistive element. The linear response of the magnetoresistive element is based on how well the resistance change of the magnetoresistive element follows the change in flux density sensed from the magnetic medium. In a disk or tape drive, a differential preamplifier is connected to the magnetoresistive element for processing the output signals from the read head.
The magnetoresistive element is a thin film layer which has its thin film faces bounded by top and bottom edges and side edges. The bottom edge, which is elongated, forms a part of an air bearing surface which flies above the plane of a magnetic disk, for example, when the disk is rotated. The magnetoresistive element is sandwiched between a pair of gap (insulation) layers which in turn are sandwiched between a pair of shield layers. The distance between the shield layers is called the gap. The smaller the gap, the greater the resolution of the MR head. The magnetic field is applied along an "easy" axis of the magnetoresistive material to improve its stability (reduction of Barkhausen noise).
One of the most desirable materials for the shield layers in a thin film magnetoresistive read head is nickel-iron (NiFe). The NiFe material is easy to fabricate and does not generate magnetic noise. However, the use of this material for the shield layers causes several problems. During fabrication of the thin film read head, it is difficult to prevent smearing of conductive material across the gap layers which separate the magnetoresistive element from the shield layers. This causes electrical shorting between the shield layers and the magnetoresistive layer at the air-bearing surface. This shorting reduces head resistances and signal amplitudes. Another problem is that it is not unusual for some portion of the head at the air-bearing surface to be at a different potential than that magnetic disk rotating therebelow. This causes a high probability of electrical arcing between the head and the disk. Both of these problems are aggravated when the flying height between the head at the air-bearing surface and the rotating magnetic disk is reduced to contact or near-contact.
The first problem of electrical shorting between the shield layers and the magnetoresistive element is overcome in the prior art by constructing one of the shield layers of Sendust. This material has two problems. The first problem is that it requires special processing during fabrication of the read head. A second problem is that it generates magnetic noise which makes quality testing of the read head difficult to perform. In contrast, shield layers constructed from the NiFe material are free from these problems. In order to construct the shield layers from NiFe the aforementioned problems need to be solved, namely: (1) shorting between the shield layers and the magnetoresistive layer at the air-bearing surface and (2) shorting between the read head at the air-bearing surface and the magnetic disk rotating therebelow.